GB1565399A

GB1565399A - Sintered cemented carbide body coated with three layers

Info

Publication number: GB1565399A
Application number: GB47625/76A
Authority: GB
Original assignee: Kennametal Inc
Current assignee: Kennametal Inc
Priority date: 1975-11-17
Filing date: 1976-11-16
Publication date: 1980-04-23
Also published as: IT1067785B; CA1083900A; DE2652440A1; US4035541A; FR2331407A1

Description

PATENT SPECIFICATION ( 1) 1 565 399

o ( 21) Application No 47625/76 ( 22) Filed 16 Nov 1976 t ( 31) Convention Application No 632608 ( 19) ( 32) Filed 17 Nov 1975 in ó ( 33) United States of America (US)

( 44) Complete Specification published 23 April 1980

U ( 51) INT CL 3 C 23 C 11/08 ( 52) Index at acceptance C 7 F IA IB 2 IB 5 2 M 2 Z 2 3 C 3 D 4 F ( 54) SINTERED CEMENTED CARBIDE BODY COATED WITH THREE LAYERS ( 71) We, KENNAMETAL INC, a corporation of the Commonwealth of Pennsylvania, United States of America, of 1 Lloyd Avenue, Latrobe, Pennsylvania 15650, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 5

Cemented hard metal carbide material is advantageously used in many products because of its inherent hardness and wear resistant properties Such cemented hard metal carbide products have found a wide variety of uses, but probably the widest known use is in cutting inserts used in metal cutting operations.

to When cutting inserts are made of carbide material and used to remove metal, 10 the metal chip being removed from the workpiece usually slides over the substrate carbide material thereby producing a frictional wear on the insert which, if it continues long enough, will break down the cutting edge of the insert and cause a cratering effect inward of the cutting edge on the cutting insert.

In this specification, reference will particularly be made to cutting inserts 15 using the triple coating according to the present invention However, carbide punches used in forming metal materials may also be coated according to the process of the present invention in order to obtain advantageous results.

Coatings for cutting inserts made from cemented carbide materials are known and the advantages of these coatings are also widely known For instance, it is 20 known that superior results can be achieved by coating the carbide cutting insert with a first coating of titanium carbide and then providing a top coating of titanium nitride over the first layer of titanium carbide The advantage found in applying titanium carbide is that the coating layer has an extreme hardness to it, yet, the titanium carbide coating does not have as good a wear resistance as that of titanium 25 nitride.

Therefore, by coating the insert with a first coating of titanium carbide, a superior hardness is achieved, and by putting the coating of titanium nitride above the coating of titanium carbide, a superior wear resistance is achieved The titanium nitride also has superior advantages in that the coefficient of sliding 30 friction between the titanium nitride coating and the metal chip being removed from the workpiece is less than when the titanium carbide coating or the bare substrate material would have when contacting the metal chip.

It is also known to put a coating of metal nitride by itself on the metal carbide substrate in order to take advantage of the more wear resistant properties of the 35 metal nitride The metal nitride, however, does not have as good a hardness as that of the metal carbide and, in addition, it has been found that, when the metal nitride coating is used by itself, it tends to spall and flake off and, therefore, does not offer the protection desired for the metal carbide substrate material.

One of the problems that is associated with any coating on a metal carbide 40 substrate is that there is a heat build-up on the coating due to the metal chips being removed from the workpiece, and coatings such as metal nitride over a metal carbide coating, as mentioned above, begin to wear or flake off after a certain period of use.

It is also known to use as a coating on such carbide substrates a metal carbo 45 nitride coating by itself in order to take advantage of the superior properties of each of the metal carbide or metal nitride compounds.

It is an object of the present invention to arrange three layers of coatings on the carbide substrate in such a manner that superior bonding is achieved between 2 1,565,399 2 the coatings and the substrate material and, also, to advantageously use the superior properties of the metal carbide in conjunction with the metal nitride.

It is a further object of the present invention to provide a carbide substrate which is also resistant to any corrosive atmosphere in which it may operate.

It is a further object of the present invention to provide a longer lasting coating 5 which will prevent the carbide substrate material from wearing away.

According to one aspect of the present invention, there is provided a coated cemented hard metal carbide product comprising: a sintered cemented metal carbide substrate; a first coating firmly and adherently bonded to said substrate and an eta (carbon deficient) phase in said substrate immediately beneath said first 10 coating, said first coating comprising a carbide of a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum and being carbon deficient so as to promote diffusion bonding-between said substrate and said coating by formation of said eta phase; a second coating bonded onto said first coating and comprising a carbonitride of said selected metal; and a third 15 coating bonded on said second coating and comprising a nitride of said selected metal; all said coatings being formed by chemical vapour deposition processes.

According to a further aspect of the invention, a method of making a coated cemented carbide product comprising the steps of heating a cemented hard metal carbide substrate material to an elevated temperature; covering said substrate with 20 a carbon-deficient first coating of a carbide of one of the metals: titanium, zirconium, hafnium, vanadium, niobium and tantalum by reacting a volatile hydrocarbon with a halide of said metal in a sub-stoichiometric amount in the presence of hydrogen, whereby an eta (carbon deficient) phase is produced in said substrate immediately below said first coating; covering said first coating with a 25 second coating of a carbonitride of said metal by reacting a volatile hydrocarbon with a halide of said metal in the presence of nitrogen and hydrogen, and covering said second coating with a third coating of a nitride of said metal by reacting a halide of said metal with nitrogen in the presence of hydrogen.

The deficiency of the carbon in the first coating causes a minute amount of 30 carbon atoms from the substrate structure to migrate into the coating and form a diffusion bond which firmly and adherently bonds the first coating to the substrate material.

The second coating, comprising a carbonitride of the selected metal from the above group, is deposited by a chemical vapour deposition process on the first 35 coating and a diffusion bond is thereby formed between the first coating and the second coating.

A final, and third, coating, comprising a nitride of the selected metal from the above group, is then deposited on the second coating by a chemical vapor deposition process so that diffusion bond again holds the third coating firmly on 40 said second coating.

The preferred method used for coating the articles is, first to elevate the temperature of the carbide material to approximately 1900 degrees Fahrenheit and then, by reacting methane gas with a metal tetrachloride using a hydrogen carrier, the first layer of metal carbide is deposited With the first layer of metal carbide 45 deposited, the metal chloride, methane and nitrogen are then reacted in the presence of a hydrogen carrier until the desired thickness of the metal carbonitride layer is achieved.

The methane is then shut off and the metal chloride is finally allowed to react with nitrogen in the presence of the hydrogen carrier to form the final metal nitride 50 coating layer on the substrate material.

The exact nature of the present invention will become more clearly apparent upon reference to the following detailed specification taken in connection with the accompanying drawing which is a schematic diagram of apparatus for carrying out the method according to the present invention 55 According to the present invention, a triple coated insert is formed having high hardness and long lasting wear characteristics by taking a cemented metal carbide substrate material and putting a first coating on the substrate, which comprises a carbon deficient carbide of a metal selected from the group of titanium, zirconium, hafnium, vanadium, niobium or tantalum (Hereinafter, when 60 the terms metal nitride, metal carbo-nitride or metal carbide are used, they refer to these compouds of one of the above-listed metals).

A second coating is put on top of the first coating, the second coating comprising a metal carbo-nitride The third and final coating, which is put over the second coating, is a metal nitride coating It has been found that this arrangement 65 enhances the hardness and wear life of a cemented metal carbide substrate material.

In the prior art, it has already been established that, with cutting tools, titanium carbide and titanium nitride have certain advantages and disadvantages when used as coatings for a cemented carbide substrate material 5 It is proposed by the present application that a longer lasting coating can be produced that takes advantage of the superior properties of both the carbide and the nitride when an intermediate coating is used between the metal carbide coating and the metal nitride coating It has been found, when a metal nitride coating is placed over a metal carbide coating on a cemented carbide metal substrate, that 10 heat which is introduced into the combined coatings will produce a thermal stress on the bonding between the metal carbide coating and the metal nitride coating.

This thermal stress is a result of the fact that the coefficient of thermal expansion is higher for the metal nitride coating is placed over a metal carbide coating on a cemented carbide metal substrate, that heat which is introduced into 15 vhe combined coatings will produce a thermal stress on the bonding between the metal carbide coating and the metal nitride coating.

This thermal stress is a result of the fact that the coefficient of thermal expansion is higher for the metal nitride coating than that of the metal carbide coating Therefore, in any application where heat is being generated by the work 20 being performed, not only will there be abrasive or frictional wear on the metal nitride coating, but the thermal stresses set up between the bonding of the two coatings will tend to break that bonding and allow the protective coating material to deteriorate rapidly.

The present invention takes advantage of the fact that, when the first metal 25 carbide coating is put on the substrate material, it will impart a superior hardness to that substrate material The first metal carbide coating is carbon deficient when applied to the substrate material so that a diffusion bond will occur between the substrate material and the metal carbide coating.

In addition, there is an advantage in that, when the carbon deficient coating is 30 put on the substrate material, carbon atoms will migrate out of the substrate material and produce an eta phase in the surface of the carbide substrate This eta phase in the carbide substrate material should be kept to a minimum such that the transverse rupture strength on the carbide substrate material is substantially not affected When kept to a minimal amount, this eta phase will, additionally, act to 35 reduce heat flow into the carbide substrate material which might create thermal deformation of the carbide substrate.

Preferably, the ratio of the carbon atoms to the metal atoms will be about 0 7 and the thickness of the first metal carbide coating will be 3 to 4 microns.

Next, the metal carbo-nitride coating is placed upon the first coating of the 40 metal carbide by a chemical vapor deposition process and diffusion bonding occurs between the second coating of the metal carbo-nitride and the first coating of the metal carbide The second coating, comprising the metal carbo-nitride coating, is, preferably, 2 to 3 microns in thickness.

The purpose of the second coating being formed of a metal carbo-nitride 45 coating is, first, that its coefficient of thermal expansion will be intermediate of the coefficients of thermal expansion of the metal carbide materials and metal nitride materials thereby reducing the thermal stress levels between the coatings of metal carbide and metal nitride The second purpose of the metal carbo-nitride coating is that it will easily form firm diffusion bonds with both the metal carbide and metal 50 nitride coatings.

The third coating is the metal nitride coating which has superior wear or crater resistance over that of the metal carbide coating The third coating is, preferably, 1 to 2 microns in thickness With the three coatings applied in this manner, the substrate material has now been provided with a superior hardness due to the initial 55 metal carbide coating and, in addition, now has a superior wear resistance due to the metal nitride coating.

It is mentioned in this application that the cemented carbide substrate is, preferably, comprised of either tungsten carbide, titanium carbide, tantalum carbide, niobium carbide or a mixture thereof, and held together by a matrix metal 60 which is, preferably, from the group of either cobalt or nickel.

In a preferred embodiment of the present invention a substrate material is used which is comprised of tungsten carbide with a cobalt metal matrix and having a first coating of titanium carbide, a second coating of titanium carbonitride and a third coating of titanium nitride Several tests have been conducted with the 65 1,565,399 preferred embodiment of the present invention, the results of which are explained in Example I below:

EXAMPLE 1

Edge Wear Edge Wear 0 007 ipr 0 015 ipr 5 sqin 250 sq in 75 sqin.

Ti C 0 0112 0 0121 0 0282 Ti C-Ti N 0 0108 0 0110 0 0257 Ti C-Ti CN-Ti N 0 0094 0 0097 0 0218 Shown above are the test results of three different coatings placed on a 10 common cemented metal carbide substrate material The first coating was a titanium carbide coating The second coating was a titanium carbide first layer coating having a titanium nitride coating superimposed on top of the first coating.

The third coating is the coating according to the present invention.

The figures represented by square inch designations are determined by 15 measuring the depth of cut by the length of the cut on a selected metal test bar The first figures above are the edge wear rate and what is measured is the deterioration of the cutting edge.

The figures are first given for a feed of 0 007 inches per revolution for two time periods The first time period, the insert at that feed rate removing 200 square 20 inches of material from the test bar and the second figures listing the conditions of the cutting edge at the conclusion of 250 square inches of material removal from the test bar.

The feed rate was then changed to 0 015 inches per revolution and results of the edge wear compared for all three coatings 25 The deterioration of the cutting edge is measured inward from the theoretical sharp edge of the cutting insert before it has been used After it has been used to remove metal, there is a rounding off effect on the cutting edge and the figures used are measuring the distance from the top of the cutting surface that is left out to where the theoretical sharp edge of the cutting insert was located in the beginning 30 As can be seen from Example I, superior edge wear resistance is achieved by the triple coating of the present invention over the coatings of the known prior art.

The above three mentioned coatings were further tested for a transverse rupture strength or an edge strength by subjecting them to a severe interrupted cut condition which was maintained until the edge of the insert fractured The results 35 of that test showed that there was no difference in the edge strength of the insert for any of the above three listed coatings.

Referring now to the drawing shown therein is a schematic diagram of the equipment used to produce a triple coated insert having for its coatings a first coating of titanium carbide, a second coating of titanium carbo-nitride and a third 40 coating of titanium nitride The chemical equations utilized by the method are as follows:

( 1) H 2 Ti CI 4 +CH 4 -Ti C+ 4 HCI H 2 ( 2) Ti C 14 + 1/2 N 2 +CH 4-Ti CN+ 4 HC 1 H 2 ( 3) Ti CI 4 +N 2- Ti N+ 4 HC 1 45 Utilizing the equations above, the coatings are produced by a chemical vapor deposition process as described below.

Referring to the drawing, there is shown therein a hydrogen supply 10, a nitrogen supply 12, a methane gas supply 14 and a hydrogen chloride supply 16.

Sequentially along a hydrogen line 18 leading from the hydrogen supply 10, there is 50 located a de-oxidizer unit 20 and a gas dryer 22, the de-oxidizer unit being used to remove any traces of air or oxygen such as may usually be found in a commercial grade of bottled hydrogen The gas dryer 22 is used to remove any water vapor from the hydrogen before the hydrogen is permitted to react with the other gases.

A low meter 24 is provided in the hydrogen line 18 to control or measure the 55 amount of hydrogen that would be necessary to produce reactions according to the above three equations.

The nitrogen supply 12 has a supply line 26, in which is located a gas dryer 28 1,565,399 and a flow meter 30, the gas dryer 28 again being used to remove any water vapor that would normally be found in a commercial grade nitrogen supply bottle The flow meter 30 is again used in the nitrogen line 26 to control the flow of nitrogen necessary for the chemical vapor deposition processes.

The methane supply 14 has a methane supply line 32, in which a flow meter 34 5 is located to control the amount of methane used in the reactions.

The hydrogen chloride supply 16 has a hydrogen chloride supply line 36 also containing a flow meter 38, to control the amount of hydrogen chloride necessary for the coating process.

In the hydrogen supply line 18 there is located a liquid metal chloride 10 vaporizer 40 provided with a heating unit 42 The liquid metal vaporizer unit is a glass lined container which contains liquid titanium tetrachloride and the heating unit 42 consists of a heated oil bath surrounding the titanium tetrachloride.

The reason for this is that the vapor pressure of the titanium tetrachloride is a function of temperature and by closely controlling the temperature, the titanium 15 tetrachloride input into the system can be controlled.

The articles to be coated are placed in a furnace 44 which has its own distribution system so that gases are fed in and distributed throughout the furnace and thereby coat the substrate materials placed therein.

A scrubber unit 46 is located at the exhaust gas exit of the furnace so as to 20 neutralize the hydrogen chloride gas that is a byproduct of the chemical vapor deposition reactions.

The steps of the coating process are as follows:

First, the metal substrate material to be coated is placed in furnace 44 and the nitrogen supply valve is turned on in order to purge the furnace of all air The 25 nitrogen is allowed to run long enough to supply a volume of nitrogen equal to twice the volume of the furnace thereby purging substantially all the air from the furnace When the air has been purged from the furnace, the nitrogen supply valve is shut off and the hydrogen supply valve is turned on.

At about the same time, the hydrogen supply valve is turned on, the 30 temperature in the furnace is elevated from room temperature to approximately 1900 degrees Fahrenheit and the hydrogen is allowed to flow through the furnace until the furnace reaches the required temn Derature When the furnace reaches the required temperature, the hydrogen supply valve is shut off and the hydrogen chloride supply valve is turned on so that the metal substrate material is precleaned 35 with hydrogen chloride vapor prior to the deposition of the first coating.

After a predetermined time, the hydrogen chloride valve is turned off and a bypass valve in a line 48 bypassing the vessel 40 is closed The hydrogen supply valve is then turned on and the hydrogen flows through the liquid metal chloride vaporizer The titanium tetrachloride is heated by the oil bath 42 to a 40 predetermined temperature to provide the necessary content of titanium tetrachloride in the hydrogen gas.

When the hydrogen carrier gas has picked up the desired amount of titanium tetrachloride, the methane supply valve is turned on and the combined gases are allowed to flow through the furnace and provide a non-stoichiometric carbon 45 deficient titanium carbide coating on the substrate material located within the furnace approximately according to the reaction Equation 1 above, which, however, applies to the production of stoichiometric Ti C When the desired coating thickness of the titanium carbide has been achieved, the nitrogen supply valve is turned on, the methane flow readjusted and the second coating of titanium 50 carbo-nitride is then deposited upon the substrate material according to reaction Equation 2 above.

When a desired thickness of titanium-carbo-nitride has been achieved, the methane supply valve is shut off and the nitrogen supply valve is adjusted so that enough nitrogen is supplied to form a stoichiometric titanium nitride coating above 55 the titanium carbo-nitride coating When the desired thickness of the titanium nitride coating has been achieved, the nitrogen supply valve is turned off and the hydrogen by pass valve is turned on to provide a flow of hydrogen gas through the furnace.

The furnace heat is then shut off and the furnace is allowed to cool down to 60 about 570 degrees Fahrenheit with the hydrogen gas flowing through the furnace.

At approximately 5700 F, the nitrogen supply gas is turned on (hydrogen off) so that the entire furnace atmosphere is charged with nitrogen as it cools from 570 degrees to room temperature.

The times necessary for depositing each layer are determined by the desired 65 1,565,399 thickness of the coating in each case As has been mentioned earlier, the preferred thicknesses of the coatings are that the first coating of titanium carbide is 3 to 4 microns, the second coating of titanium carbo-nitride is 2 to 3 microns and the third coating of the titanium nitride is 1 to 2 microns.

The cemented metal carbide substrate, when coated according to the present 5 invention, has extreme hardness and tough wear resistant properties and, in addition, the carbide, carbo-nitride and nitride coating are extremely resistant to corrosive atmospheres Thus, the coated cemented metal carbide substrate is ideal for many uses and applications other than in the metal cutting industry.

The preciseness with which the thickness of the coating may be controlled 10 allows it to be used to "build-up" parts made from a cemented metal carbide material that have worn a small amount and where the small amount of wear would be critical to the operation.

Claims

WHAT WE CLAIM IS:-

1 A coated cemented carbide product comprising: a sintered cemented metal 15 carbide substrate; a first coating firmly and adherently bonded to said substrate and an eta (carbon deficient) phase in said substrate immediately beneath said first coating, said first coating comprising a carbide of a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum and being carbon deficient so as to promote diffusion bonding between said substrate 20 and said coating by formation of said eta phase; a second coating bonded onto said first coating and comprising a carbonitride of said selected metal; and a third coating bonded on said second coating and comprising a nitride of said selected metal; all said coatings being formed by chemical vapour deposition processes.

2 A coated cemented carbide product according to Claim 1, in which the 25 cemented carbide substrate comprises a metal selected from the group of tungsten carbide, titanium carbide, niobium carbide, tantalum carbide or a mixture thereof and a matrix metal selected from the group of cobalt or nickel.

3 A coated cemented carbide product according to Claim 1, in which said first coating has a thickness of 3 to 4 microns 30 4 A coated cemented carbide product according to Claim 3, in which said second coating has a thickness of 2 to 3 microns.

A coated cemented carbide product according to Claim 3 or Claim 4, in which said third coating has a thickness of 1 to 2 microns.

6 A coated cemented carbide product according to Claim 2 or any one of 35 Claims 3 to 5 as appendent thereto, in which said substrate comprises tungsten carbide and a cobalt matrix.

7 A coated cemented carbide product according to any one of the preceding Claims, in which said first coating is carbon-deficient titanium carbide.

8 A coated cemented carbide product according to Claim 7, in which said 40 second coating is titanium carbonitride.

9 A coated cemented carbide product according to Claim 8, in which said third coating is titanium nitride.

A method of making a coated cemented carbide product comprising the steps of heating a cemented hard metal carbide substrate material to an elevated 45 temperature; covering said substrate with a carbon-deficient first coating of a carbide of one of the metals: titanium, zirconium, hafnium, vanadium, niobium and tantalum by reacting a volatile hydrocarbon with a halide of said metal in a substoichiometric amount in the presence of hydrogen, whereby an eta (carbon deficient) phase is produced in said substrate immediately below said first coating; 50 covering said first coating with a second coating of a carbo-nitride of said metal by reacting a volatile hydrocarbon with a halide of said metal in the presence of nitrogen and hydrogen; and covering said second coating with a third coating of a nitride of said metal by reacting a halide of said metal with nitrogen in the presence of hydrogen 55 11 A method according to Claim 10, in which said carbon deficient first coating has a metal-to-carbon atomic ratio of about 1 to 0 7.

12 A method according to Claim 10 or Claim 11, in which said metal selected from said group is titanium.

13 A method according to any one of Claims 10 to 12, in which said volatile 60 hydrocarbon is methane.

14 A method according to Claim 13, in which said metal halide is titanium tetrachloride.

1,565,399 ( 1 7 1,565,399 7 A coated cemented carbide product as claimed in Claim I and substantially as hereinbefore described.

16 A method of making a coated cemented carbide product substantially as hereinbefore described with reference to the drawing.

For the Applicants G.F REDFERN & CO.

Marlborough Lodge 14 Farncombe Road Worthing West Sussex Printed for Her Majesty's Stationery Office, by the Courier Press Leamington Spa 1980 Published by The Patent Office, 25 Southampton Buildings London WC 2 A IAY, from which copies may be obtained.